Method of fabricating arrays of individually oriented micro mirrors for use in imaging security devices

ABSTRACT

A visual display assembly useful as an authentication or anti-counterfeiting element. The assembly includes a substrate and, on a surface of the substrate, an array of micro mirrors receiving ambient light. Each mirror includes a reflective surface to reflect the ambient light to display an image that appears to float in a plane, which is spaced a distance apart from the surface of the substrate. The image includes a plurality of pixels, and the array of micro mirrors includes for each of the pixels a set of the micro mirrors each having a reflective surface oriented to reflect the ambient light toward a point on the plane corresponding to one of the pixels. Each of the sets of the micro mirrors includes a plurality of the micro mirrors, and the reflected ambient light each set of micro mirrors intersects to illuminate or write a pixel of an image.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/203,128, filed Nov. 28, 2018, which is a divisional of U.S. patentapplication Ser. No. 15/162,113, filed May 23, 2016, that claims thebenefit of U.S. Provisional Application No. 62/262,767, filed Dec. 3,2015, which are all incorporated herein by reference in theirentireties.

BACKGROUND 1. Field of the Description

The present invention relates, in general, to anti-counterfeitingdevices for currency and brand authentication, and, more particularly,to currency and brand authentication elements, and methods of designingand manufacturing such authentication elements, that are configured toprovide a multi-planar image that is viewable without special eyewearand that is difficult, if not nearly impossible, to replicate or copy.

2. Relevant Background

Anti-counterfeiting efforts often involve use of an anti-counterfeitingdevice or element that is made up of an array of lenses and an imageprinted onto the back of the lens array or onto an underlying substrateor surface (e.g., a sheet of paper or plastic). The anti-counterfeitingelement may be used to display an image that is chosen to be unique andbe an indicator that the item carrying the anti-counterfeiting elementis not a counterfeit. The anti-counterfeiting market is rapidly growingworldwide with anti-counterfeiting elements placed on a wide range ofitems such as upon currency (e.g., on a surface of a paper bill to helpprevent copying) and on labels for retail products (e.g., labels onclothing showing authenticity).

In this regard, moiré patterns have been used for years inanti-counterfeiting elements with arrays of round lenses and with arraysof hexagonal lenses (or round and hexagonal lens arrays). Typically, theprinted images provided in an ink layer under these lens arrays aresmall, fine images relative to the size of the lenses. A moiré patternis provided in the printed images in the form of a secondary andvisually evident superimposed pattern that is created when two identicalpatterns on a surface are overlaid while being displaced or rotated asmall amount from each other.

In such moiré pattern-based anti-counterfeiting elements, some of theimages may be printed in a frequency slightly more or less frequent thanthe one-to-one dimension of the lenses in two axes, and some of theimages may be printed slightly differently relative to each other. Whilehelpful to reduce counterfeiting, use of moiré patterns with round lensarrays has not been wholly satisfactory for the anti-counterfeitingmarket. One reason is that the effects that can be achieved with moirépatterns are limited, and the effect is often relatively easy to reverseengineer, which limits its usefulness as an anti-counterfeiting element.For example, printing the underlying image is becoming easier toaccomplish due to high resolution lasers and setters and other printingadvances. Typically, for an element, the micro-lenses are printed usingan emboss and fill technology, which limits the printing to one colordue to the fact that the process tends to be self-contaminating afterone color and also due to the fact that the process is difficult tocontrol from a relative color-to-color pitch in the emboss-and-fillprinting process.

In other cases, holograms and lens features are used for securitydevices in currency, brand authentication and brand protection as wellas on high security documents. Holograms are becoming increasingly lesssecure, in part, due to the rise in technology, programming, and generalavailability of programs that allow one to easily create holograms. Inmany applications, the cheaper dot matrix holograms are “good enough” tosimulate many of the effects of the more expensive elaborate hologramsused in anti-counterfeiting elements. While lens features done properlycan be more secure than hologram elements, there is a need for newtechnology to combat the currency and product counterfeiting. Ideally,new technology would have attributes that are not possible withholography or micro-lenses.

Hence, there remains a need for advancements in the design andfabrication of assemblies or elements that display imagery useful foranti-counterfeiting and/or product/document authentication. For example,such improvements may allow new anti-counterfeiting devices or elementsto be produced for use with currency, labels, credit/debit cards, andother items, and these anti-counterfeiting devices preferably would bemuch more difficult if not nearly impossible to duplicate or copy.Further, there is a growing demand for such anti-counterfeiting devicesto provide a surprising or “wow factor” with their displayed imagerysuch as images that float above and/or below a focal plane (e.g., moretrue 3D displays) rather than merely laterally reflecting back lightsuch as with a sequence of mirrors or mirrored surface or usingreproducible holograms.

SUMMARY

Briefly, the inventors recognized that an anti-counterfeiting orsecurity device can be provided that is configured to “write” imageswith light in one, two, or more spatial planes above and below thesurface of an array of micro mirrors. Each of the micro mirrors isoriented (or “programmed”) to act with a number of other such micromirrors (e.g., a “set of pixel-providing micro mirrors”) as one pixel inthe written image(s) as the set of micro mirrors each directs itsreflected light to a particular location in the image(s) displayplane(s) (e.g., an apex of a cone with each of the micro mirrors in theset of pixel-providing micro mirrors being within the base of the cone)that when viewed with a number of other such pixels (each provided by adifferent set of pixel-providing micro mirrors) makes up a written imagein one or more spaced apart image display planes.

In other words, text, imagery, and so forth can be written with ambientlight by focusing the micro-mirrors to different spatial planes abovethe plane of the security device (which is typically provided on asurface of a document (e.g., currency) or product being authenticatedwith the security device). Conversely, the technology can then “reverse”to the viewer by having the “bright” pixels go to “dark” and thebackgrounds reverse from “light” to “dark” with a change of perspective(e.g., occurring when the viewer changes their viewing angle or rotatesthe document/product containing the security device).

Also, since the technology is made of mirrors (made from thin aluminum,silver or gold depositions on an upper surface of the document/producton which the security element is provided (e.g., any supportingsubstrate)), the anti-counterfeiting or security device will work fromtwo sides in a film process (e.g., when the supporting substrate istransparent). This type of two-sided or two-view image cannot be donewith holography or other presently available anti-counterfeitingtechnologies. The technology can be embossed into films, metallized, andthen processed into currency threads, foil stamps, labels and packaging.It can also be directly stamped onto coins or other metallic surfaces(e.g., provided on nearly any supporting substrate). Color can also beadded to the displayed or “written” image(s) by using a reflective inkprinting method or with the use of dielectric nanostructures (e.g., withplasmonic resonance and/or other techniques).

More particularly, a visual display assembly is provided that is usefulas a security element on paper and coin currency, product labels, andother objects. The assembly includes a substrate (which may be part ofthe object upon which the security element is provided such as a pieceof currency or a product label). The assembly also includes, on asurface of the substrate, an array of micro mirrors receiving ambientlight and, in response, displaying an image in a plane spaced a distanceapart from the surface of the substrate. The image includes or is“written” with a plurality of pixels, and the array of micro mirrorsincludes for each of the pixels a set of the micro mirrors each having areflective surface oriented to reflect the ambient light toward a pointon the plane corresponding to one of the pixels.

In some embodiments, each of the sets of the micro mirrors includes atleast twenty of the micro mirrors (e.g. a number in the range of 20 to40 such as about 30 mirrors). To provide a “bright” or light pixel, thereflected ambient light from the twenty or more micro mirrors intersectsor crosses at (or passes near to) the point corresponding to the one ofthe pixels (e.g., each pixel is displayed or lit by beams/rays fromreflective surfaces of the micro mirrors crossing at a common point onthe image display plane). The point on the plane may correspond to anapex of a cone, and the twenty or more micro mirrors can be locatedwithin a base of the cone coplanar with the surface of the substrate.The micro mirrors within the base of the cone but excluded from (or notincluded in or used for) the set of the micro mirrors displaying thepixel are oriented to reflect the ambient light away from point on theplane corresponding to the pixel to provide a dark background for theimage.

The assembly may be configured to display images in more than one imagedisplay plane or in two or more levels/layers. In this regard, the arrayof mirrors may be configured to behave further in response to thereceiving of the ambient light to display a second image in a secondplane spaced a distance apart from the plane displaying the image. Thesecond image may be provided or “written” with a plurality of pixels (aswas the case with the first image). The array of micro mirrors includes,for each of the pixels of the second image, a set of the micro mirrorseach having a reflective surface oriented to reflect the ambient lighttoward a point on the second plane corresponding to one of the pixels ofthe second image. The first image has a first viewing angle and thesecond image has a second viewing angle offset from the first viewingangle by at least 10 degrees (such as an offset angle in the range of 10to 45 degrees with offset angles of 20 to 30 degrees being useful insome embodiments).

In some particular implementations, the substrate is transparent,whereby the image is displayed to be spaced apart the distance from afirst side of the substrate and further whereby a second image includinga second set of pixels is displayed by the array of micro mirrors to bespaced apart a second distance from a second side of the substrateopposite the first side. In this manner, the array of micro mirrors canbe said to be completely functional on the reverse side of the substrate(or film) to present a mirror image or a reverse image (in the imageplane) to the viewer on the opposite side of the substrate.

In the same or other embodiments, the micro mirrors are rectangular(e.g., square) with a smallest side having a length of at least 35microns such as 50 microns or more while other embodiments use mirrorsthat are circular with a diameter of at least 35 microns (e.g., 50microns or larger in diameter). In practice, the plane in which theimage is displayed may be above, below, or coinciding with the focalplane for the array of the micro mirrors. Also, the image may bedisplayed using only (or mostly) white light (and off or dark pixels) orthe micro mirrors may be configured to display the image with colors (inaddition to white). This may be achieved with at least one of ink,plasmonic resonance, and dielectric material being used to configure themicro mirrors to display the image with the desired colors.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top perspective, partial view of a visual display assemblyfor use as an anti-counterfeiting element or device showing a singlemicro mirror that would be provided in an array of such micro mirrors;

FIG. 2 is a side view (e.g., a functional schematic) of an object (suchas currency, a document, a financial card, or the like) including ananti-counterfeiting or authentication (or security) element/device ofthe present description;

FIG. 3 is an enlarged view of a subset of the micro mirrors of thesecurity element of FIG. 2 corresponding to micro mirrors in an area ofone cone base associated with one cone apex or written pixel in one ofthe displayed/written images provided by the security element of FIG. 2;

FIG. 4 is a schematic or graphic side view or diagram of a securityelement during its use to provide a two-layer or level image;

FIG. 5 is a side schematic view or diagram of a security element duringits use to provide a display that combines a light image and a darkimage;

FIG. 6 is a functional block diagram of a computer or computing deviceconfigured to run an array design program to allow an operator togenerate a design of an array of micro mirrors for displaying aparticular image(s) when provided in a security element;

FIG. 7 is a flow diagram of an exemplary design method for an array ofmicro mirrors for use in a security element, such as may be carried outby operation of the system of FIG. 6;

FIGS. 8A and 8B illustrate a micro mirror design GUI that can bedisplayed on a monitor or display by the design program;

FIGS. 9A-9C are graphs illustrating images that can be displayed onvarious levels or image display planes by an array of micro mirrors ofthe present description;

FIG. 10 is a plot illustrating a ray tracing near a first image displayplane or first level/layer for one modeled array of micro mirrors;

FIG. 11 illustrates a representative GUI or ray tracing menu that allowsa user to specify parameters to utilize in performing the ray tracing;

FIG. 12 is a plot of a representative ray tracing showing beams/raysreflected from micro mirrors in a mirror plane and converging on aviewer's retina;

FIGS. 13A and 13B illustrate written or displayed images provided by anarray of micro mirrors with an angular offset between image displayplanes or levels/layers of the imagery;

FIGS. 14A and 14B illustrate plots of floating pixels in a space abovean array of micro mirrors; and

FIGS. 15A and 15B illustrate plots generated and displayed by a previewprogram (which may be a subroutine of the design program describedherein) for previewing likely or predicted results of a design of anarray of micro mirrors.

DETAILED DESCRIPTION

Briefly, the present description is directed toward visual displayassemblies that can be used as anti-counterfeiting or authenticationelements or devices such as on currency, coins, documents, products, andso on. Each visual display assembly includes an array of a large numberof micro mirrors, and this array can be provided on a surface of nearlyany supporting substrate (e.g., a surface of a piece of currency, on acoin, on a surface of a product or its sales/identification label, andso on). Sets (or subsets) of the micro mirrors are used to work inunison to “write” pixels of images in one, two, or more image displayplanes above the supporting substrate by having each of the micromirrors in each of the pixel-providing sets direct light striking itsfirst or upper reflective surface to a location of a pixel in one of theimage display planes. The sets of pixels may be configured to provideangular offset viewing (e.g., by an offset angle in the range of 15 to35 degrees or the like with 20 degrees used in some cases between theviewing angles of the written images of each adjacent image displayplane) in the different image display planes such that a viewertypically only observes or perceives the written pixels of one imagedisplay plane at a time (or at a single viewing angle or perspective)and switching occurs as the viewer changes their viewing angle orrotates the substrate supporting the visual display assembly and itsmany micro mirrors.

The visual display assembly (or security element/device) is designed tocreate a floating image(s) of pixels, and the pixel-providing sets ofmicro mirrors are chosen to have a large enough number to effectivelydisplay a great enough quantity of light to allow a viewer to perceiveeach separate, floating pixel in the written or displayed image. Thenumber of micro mirrors used in each set may vary due to a large numberof parameters such as material used to provide the reflective uppersurface, size of each micro mirror (e.g., with 35 to 100 micron mirrorsused in some implementations and 50 micron mirrors used in one prototypeof the present invention), and the like. Each of these micro mirrors ineach pixel-providing set is oriented to try to have all of these micromirrors direct their reflected light to intersect at a point (thewritten pixel of the displayed image) in an image display plane abovethe supporting substrate, and each pixel of the written image is eitheron or off (or providing light or no light) at various viewing angles.

A basic or underlying idea of the micro mirror-based visual displayassembly is to use ambient light and a plane (an upper surface of asupporting substrate) containing many, small mirrors. The ambient lightthat is reflected off the mirrors is aimed or targeted toward desiredpoints (or pixels) above the plane that contains the mirrors. The imagedisplayed by all the pixel-providing sets of micro mirrors targeting afirst image display plane above the supporting substrate may beconsidered a first layer image. The first layer image can be defined byartwork that has light or dark pixels to be produced in this first layer(or a multi-layer image) or first image display plane. To this end, themirrors in a pixel-providing set of micro mirrors are carefully selectedfrom the micro mirror array as being within a circle (or cone base)defined by the intersection of the cone defined by an apex angle and apixel from the desired image display plane/layer (e.g., the first imagedisplay plane) that is chosen to coincide with the apex of the cone.Each of these mirrors (which are in the base of the cone) is then aimedor targeted (or “oriented”) toward the cone apex (image's pixel) so thatthe resulting effect is a point source of light floating a height ordistance above (or below in some cases) the plane of the supportingsurface containing the array of micro mirrors at the location of thepixel.

Prior to explaining a design or configuration of an entire array ofmicro mirrors in a visual display assembly, it may be useful to firstlook at a single one of these mirrors. FIG. 1 illustrates a portion of avisual display assembly 100 (or a substrate with a security element ordevice) according to the present description. As shown, a supportingsubstrate 110 with a surface 112 is provided that receives and supportsa micro mirror 120. For example, the substrate 110 may be a piece ofcurrency, a coin, a product label, a document, a credit/debit/bank card,or the like for which it is desired to provide anti-counterfeiting orauthentication functionality with the visual display assembly orsecurity element 100. The micro mirror 120 is shown to include a body(or lower layer/surface) 122 that is affixed to or integrally formedwith the surface 112 of the substrate 110. The view in FIG. 1 is only“partial” as it will be understood that the assembly 100 typically wouldinclude many (e.g., hundreds to many thousands) of the micro mirrors 120(i.e., an array of micro mirrors 120). Each of such micro mirrors 120 isindividually oriented or “programmed” as discussed below such that themicro mirrors 120 of the array act together to display one or morefloating images made up of a plurality of pixels in one or more imagedisplay planes above the substrate surface 112.

The micro mirror 120 also includes an upper (or exposed) reflectivesurface 124 facing away from the surface 112 of the supporting substrate110. This surface 124 is reflective as the micro mirror 120 typicallywill be formed of a metal or metallic compound or other material chosenfor its reflective properties. For example, the micro mirror 120 may bea thin layer of aluminum, silver, gold, or the like provided bydeposition upon the surface 112 of the substrate 110. When the imagedisplay assembly 100 is in use, ambient light 130 strikes the reflectiveupper surface 124 of the micro mirror 120 and is reflected as shown at134 from the upper surface 124. Particularly, the micro mirror's uppersurface 124 is to have a normal vector 135 (e.g., as may be defined asoutput of a design program with X, Y, and Z coordinates), and theincoming ray 130 and the normal vector 135 from the same angle, (3, asis formed between the normal vector 135 and the reflected light 134.

The reflected light 134 is preferably directed or aimed so as to crossan image display plane 140, which is spaced apart a height, H₁, above oraway from the substrate surface 112 (and reflective surface 124 whichmay be substantially coplanar due to the small thickness of the body122), at a location (X-Y-Z coordinates may define this location relativeto the surfaces 112 and 124) coinciding with or defining one of aplurality of written pixels 142 of an image displayed by the assembly100 in the plane 140. While not shown, a plurality of other micromirrors configured similar to mirror 120 would also reflect theirreceived ambient light to the point/pixel 142 in the plane 140 (aplurality of reflected light beams from micro mirrors would intersect atthe point/pixel 142) so as to provide a point source of light at 142viewable by a viewer 102.

To provide this desired reflection of light 134, the micro mirror 120 isoriented or has its reflective surface 124 oriented in a particular,predefined (e.g., by a visual display assembly configuration computerprogram or algorithm) manner. Particularly, each micro mirror 120 may beindividually oriented by rotating its body 122 (or surface 124) aboutone or both of first and second rotation axes 150, 152 as shown witharrows 151, 153 during design processes (prior to fabrication). Then,the micro mirror 120 may be formed with these design parameters so thatthe reflective upper surface 124 (with its known location in the arrayof micro mirrors by X-Y coordinates of its center) is oriented (at firstand second angles) relative to the two axes 150, 152 to have its normalvector 135 aimed or targeted in a particular manner (X-Y-Z coordinatesof the normal vector for the mirror 120), e.g., to have ambient light130 reflected as shown at 134 to cross the image display plane 140 atthe location of the pixel 142. As noted above, the size (and shape) ofeach micro mirror 120 may be varied to practice the invention with someembodiments utilizing square-shaped bodies 122 that have sides with alength, L_(side), that is typically greater than about 35 microns (suchas 50 microns) and often in the range of 40 to 60 microns while someembodiments may use larger micro mirrors.

FIG. 2 is a side view (e.g., a functional schematic) 200 of an object(such as currency, a document, a financial card, or the like) 210including an anti-counterfeiting or authentication (or security)element/device 220 of the present description. The object or substrate210 includes an upper or first surface 212 upon which is provided orformed the security device 220 (which may take the form of the visualdisplay assembly 100 of FIG. 1). The security device 220 has an exposedor upper surface 222 that is configured to provide an array of micromirrors 224, which may be individually oriented to provide reflection ofambient light striking the surface 222 of the security element 220 so asto display one or more floating images that can be observed by a viewer202 to authenticate the object 210.

To this end, a first number of the micro mirrors 224 may be configuredto provide sets of pixel-providing micro mirrors that reflect ambientlight as shown with arrows 230 to “write” or display a first displayedimage 242 made up of a plurality of pixels 243 (with each of thesepixels 243 associated with one of the sets of pixel-providing micromirrors 224). A second number of the micro mirrors 224 is configured toprovides sets of pixel-providing micro mirrors that reflect ambientlight as shown with arrows 250 to “write” or display a second displayedimage 262 made up of a plurality of pixels 263 (with each of thesepixels 263 being associated or written by one of the sets ofpixel-providing micro mirrors 224). As discussed with reference to FIG.1, each of the micro mirrors 224 in the same set of pixel-providingmicro mirrors 224 used to create/write a particular pixel 243, 263 inone of the images 242, 262 is configured or oriented with its reflectivesurface oriented (with rotation relative to one and/or two rotationaxes) to target or direct a point/location on the plane 240 or 260coinciding with the pixel 243, 263. This, in most embodiments, coincideswith an apex of a cone with each of the pixels 243, 263 in the set ofmicro mirrors 224 being in the base of the cone (e.g., within thecircular area on the surface 222 defined by the cone base). Note, eachof these micro mirrors 224, though, is oriented uniquely and differentlyto provide the reflected light 230, 250 along a normal vector to itsreflective surface.

To the viewer 202, the first displayed image 242 appears to float in thefirst image display plane 240 that is a height, H₁, above the surface212 of the object/substrate 210 while the second displayed image 262appears to float in the second image display plane 260 that is adifferent (typically greater) height, H₂, above the surface 212. Themicro mirrors 224 are oriented so that the pixels 243 of the first image242 are a viewing angle offset, θ_(Offset), (e.g., 10 to 30 degrees orthe like) from the pixels 263 of the second image 262 so that the viewer202 typically only views one of the floating images 242, 262 at a time(at a range of viewing angles).

As discussed above, micro mirrors for each set of pixel-providing micromirrors are chosen from a set of available micro mirrors located withinan area on the security element surface (or substrate surface) thatcorresponds with a base of the cone with an apex coinciding with thepixel being created by these micro mirrors. FIG. 3 is an enlarged viewof a subset of the micro mirrors 224 on the surface 222 of the securityelement 220 of FIG. 2, which correspond to micro mirrors 224 in an areaof one cone base with diameter, Diam_(Cone Base), associated with onecone apex or written pixel 243 or 263 in one of the displayed/writtenimages 242 or 262 provided by the security element 220.

FIG. 3 illustrates all the available micro mirrors 224 in the cone base,but the security element 220 typically is designed so that only a subsetof these available mirrors 224 (such as 20 to 40 or more with 30 shownin use in FIG. 3 at 324) are used to write or display a particularpixel. The unused mirrors 224 typically are oriented to reflect receivedambient light away from the location of the pixel being written/createdby the chosen mirrors 324, which may be considered as providing a maskwith the unused mirrors 224. The chosen mirrors 324 (or mirrors in theset of pixel-providing micro mirrors) are shown with shading/patterningthat would not be actually present in a security element but that isuseful for differentiating these mirrors 324 from the other/unused onesof the mirrors 224.

As will be explained below, the micro mirrors 324 in the set ofpixel-providing micro mirrors are randomly chosen such that the mirrors324 do not provide an obvious, regular pattern and each pixel's set ofmicro mirrors 224 likely will have a very different pattern within acone base or circular area of the surface 222 of the security element220. Also, each of the micro mirrors 324 in the set used to provide aparticular pixel 243 or 263 will be differently oriented so as to havethe normal vectors of all the mirrors 324 intersect at the X-Y-Zcoordinates of the same pixel 243 or 263 in the appropriate one of theimage display planes 240 or 260.

Significantly, the mirrors 324 are not pointing toward a viewer but,instead, are aimed or targeted toward the intersection point (or pixelcoordinates) in the image display plane or layer. The use of sets ofmicro mirrors to provide or create floating pixels that in combinationcan write or display an image in one, two, or more layers is effectivein providing a displayed image with depth and with high contrast.Further, the image appears to switch from light to dark with rotation ofthe object/substrate with the security element (or with movement of theviewer's eyes to change their viewing angle or perspective).

FIG. 4 is a schematic or graphic side view or diagram 400 of a securityelement 410 during its use to provide a two-layer or level image. Thesecurity element 410 includes a micro mirror array 412 made up ofnumerous (e.g., thousands) micro mirrors (e.g., 50 micron diametermirrored surfaces). As shown, three sets of micro mirrors in the array412 have been oriented or configured to display pixels 422 in a firstplane or at a first level 420 above the security element 410 (or itssurface containing the array 412). As shown with arrows 423, light isreflected so that beams from a set of the micro mirrors intersect tocreate a pixel 422 in the first level 420. These are provided within acone angle, β_(Cone), Further, as shown with arrows 425, a mask or maskimage may defined to block some rays by having the mirrors that wouldprovide this light directed outside of the conical angle, β_(Cone),region (e.g., the arrows 425 are associated with light that is notactually reflected for viewing with the light 423 but is, instead,directed elsewhere).

Also, as shown two sets of micro mirrors in the array 412 have beenoriented or configured to display pixels 432 in a second plane or at asecond level 430 spaced apart from level 420. Arrows 433 represent beamsof reflected light that are directed from these sets of mirrors tointersect or cross at the locations of the pixels 432. Also, as shown,the pixels are displayed to the viewer at viewing angles that are offsetby an angle (pixel offset angle), γ (such as 10 to 30 degrees or thelike). The basic angle direction of the pixels 432 is chosen to offsetthe image in the plane/level 430 for the viewer (or at the viewer) fromthe image in the plane/level 420.

FIG. 5 is a schematic or diagram 500 similar to that of FIG. 4 butshowing an embodiment of a security element 510 with an array of mirrorsadapted specifically to provide two light and dark images. The diagram500 illustrates that the sets of pixel-providing micro mirrors on thesecurity element 510 (or in a mirror planar surface) can be oriented toprovide a light image (with bright pixels with a dark background) thatwhen going in reverse provides a dark image with a light background asthe viewer rotates the element 510 or otherwise changes theirperspective.

As shown, the security element 510 has a planar mirror surface with anarray of micro mirrors adapted to reflect light in directed beams 514and 518. The beams/rays 514 are directed so as to display/create pixels522 on a first plane 520 that is more proximate to the mirror plane ofsecurity element 510 (with only two pixels 522 shown in each image plane520 and 530 (in each displayed image) for clarity with it beingunderstood that any number of pixels (1 to more typically many (e.g., afew hundred to several thousand or the like)) may be used to create eachimage with the size of the mirrors and overall array provided insecurity element 510 being the only limitations). The beams/rays 518provided by the other sets of pixel-providing mirrors in element 510 aredirected/aimed to cross/intersect on the second image displaying plane530 (which is spaced apart from the first plane 520 some distance such0.25 to 1 inch to several inches or more) to display/create pixels 532.

To make the images provided by the pixels 522, 532 appear light anddark, the beams 514 and 532 are separated by an angle, ϕ, (e.g., 15 to30 degrees or more) as may be measured between proximate ones of thebeams in each group 514 and 518 (e.g., after the beams cross proximateto the mirror plane of security element 510 such as at or after thefirst image display plane 520). The angle of image separation, ϕ, andthe cone angles at pixels 522, 532 are chosen to give this angularseparation. Images of bright and dark zones do not overlap, and imagesprovided by pixels 522 and 532 appear to the viewer to be in the twospaced apart or different planes 520, 530. One image darkens as theother lightens as the view angle changes.

FIG. 6 is a functional block diagram of a computer or computing device600 configured to run an array design program to allow an operator togenerate a design of an array of micro mirrors for displaying aparticular image(s) when provided in a security element (e.g., toperform steps of the method of manufacturing a security element with anarray of micro mirrors according to the present description). Thecomputer 600 includes a processor(s) 610 that executes code/instructionsin computer readable media to run or provide the functionality of themicro mirror array design program 630 as well as those of the raytracing module(s) 635. The processor 610 also manages operation ofinput/output (I/O) devices 620 such as a keyboard, a mouse, a touch pador screen, voice recognition software, and the like configured to allowa user to provide input such as to select design parameters for aparticular security element. The I/O devices 620 may include amonitor/display 624 and the design program 630 may be configured togenerate one or more graphical user interfaces (GUIs) 628 displayed onthe monitor/display device 624 to facilitate a user providing input andto display calculated results (such as the calculated angularorientations of each mirror in the array).

The processor 610 during the running of the design program 630 mayaccess and manage memory (or data storage device) 640, which may beonboard as shown or offboard but accessible by the processor 610. Theoutput of the design program 630 is stored at 650 in memory 640 andprovides a design for an array of micro mirrors for a particularsecurity element to be manufactured. The design 650 is shown at 651 toinclude a calculated angular orientation for each mirror in the array.This may be defined at 652 with a center location of the mirror (e.g.,X-Y coordinates) combined with coordinates of a normal vector (e.g.,X-Y-Z coordinates) for the mirror. This information can be used in amanufacture (e.g., deposition or other processes) of a security elementfor an object (such as for currency, coins, product labels, documents,and the like).

To allow the design program 630 to generate the array design 650, a usertypically initially chooses a digital image 660 as a base or startingimage for creating an anti-counterfeit or authentication image to bedisplayed in one or more planes or levels relative to the array of micromirrors. The user/operator then may use the GUI 628 or other I/O devices620 to identify one or more images to be displayed on each level of theimage displayed by the security element being designed as shown at 662,663. For example, images in the first plane or level 662 may beforeground images in the base/start image 660 while images 663 in thesecond (or later) plane or level 663 may be background (or intermediate)images of the base/start image 660. The design program 630 or anotherprogram on the computer 600 or available to the processor 610 may thenbe used to convert the digital base/start image 660 into a text or otherfile that identifies each pixel in the base/start image as beingassigned to a particular one of the levels/planes (e.g., a text filewith a plurality of numbers replacing the pixels of the image 660representing one of the planes/levels of the image to be displayed bythe security element being designed using the design program 630).

At this stage of operations, the design program 630 may function togenerate a GUI 628 with a number of data entry boxes/fields promptingthe user to accept default design parameter values or to enter/modifysuch values. The design program 630 may then operate to calculate thearray design 650 including the angular orientations of each of the micromirrors in an array. For example, the user may set or define a coneangle, as shown at 666 in memory 640, for use for generating the pixelsof images in each level/plane used to display a security image. The coneangle often will differ for each level such as with larger valuesassigned to earlier/lower levels/planes (but this is not required), andexemplary cone angles for image pixels may be in the range of 10 to 30degrees or the like.

The user may also be asked to provide or select an angular offsetbetween each pair of image levels/planes as shown at 668 in memory 640,and this offset may range from 0 to 30 or more degrees to achieve adesired effect for a displayed image. Other parameters that may beentered or set by the user of the system 600 may include the dots perinch (DPI) 670 that defines the spacing of the pixels in each imagedisplay level or plane (the cone apex planes). The user may also beallowed to set the number mirrors to be used to create or display eachpixel as shown in memory 640 at 680 (with 20 to 40 mirrors likely to beuseful in some implementations). Further, the user may define heights ofthe image display levels or planes as shown at 688 (such as a firstplane at 10000 microns, a second plane at 20000 microns, a third planeat 30000 microns or other useful spacings/heights).

With the parameters defined, the user may instruct the design program630 to run to first choose, for each pixel in each image to be displayedin the levels/planes, a set of micro mirrors to be used to display orcreate the pixel. The other pixels may be considered unused pixels orpixels that can be used in a mask, and these pixels may be angularlyoriented to direct light outside of the cone angle. The design program630 may then continue with determining an array design 650 with thesesets of pixel-providing mirrors 684 by calculating for each of the micromirrors of the array its angular orientation 651, which may be providedby the coordinates (e.g., X-Y coordinates or the like) of the center ofeach mirror and the coordinates (e.g., X-Y-Z coordinates or the like) ofthe normal vector for the mirror with such center coordinates. Thisdetermination of the design 650 is carried out such that the micromirrors in each set of pixel-providing mirrors is oriented to direct itsreflected ambient light (a reflected light stream or beam or ray) ontothe same image display plane at the same location (e.g., at a locationof a pixel). The ray tracing module 635 may be configured to test theeffectiveness of the array design 650 as explained below to ray tracereflected light providing images to a viewer's eye (or expected viewingpositions relative to a security element with the array of micro mirrorshaving angular orientations as called out in the array design 650).

FIG. 7 is a flow diagram of an exemplary design method 700 for an arrayof micro mirrors for use in a security element, such as may be carriedout by operation of the system 600 of FIG. 6. The method 700 starts at705 such as with loading a design program onto a computing device andinitiating or running the program. The method 700 continues at 710 withselecting a base or start image such as selecting a file in memory of acomputing device providing a digital image of objects that may be usefulfor providing a multi-layer display for use in authenticating an object(e.g., an image with one or more components that can be presented asforeground images and one or more components that can be presented asbackground and/or intermediate images or on layers that appear behindthe foreground images).

In step 720, the method 700 involves a user indicating whichportions/components of the base/start image from step 710 should bepresented in the image(s) displayed on each of the one, two, or moreimage display layers for this security element. Hence, step 720 may bethought of as including first deciding how many display layers/planes touse with this array of micro mirrors (and this value can be affirmed/setin later step 730 as one of the design parameters). Step 720 may involveassigning differing colors of a colored base/start image to differingimage display planes/levels. In other cases, a component/object in theimage may be chosen as a foreground image and one or more of the othercomponents/objects in the image may be selected to be background imagesto be on different levels/planes. At step 725, the method 700 continueswith converting the base image into a file (such as a text document orfile with each pixel replaced with 0's and 1's when two levels/planesare used and so on) that indicates for each pixel in the base imagewhich level/plane that pixel is assigned for display by the array ofmicro mirrors.

The method 700 continues at 730 with the user choosing/setting designparameters (or accepting default ones such as may be predefined by thedesign program or as previously saved for other arrays). For example,the spacing of pixels in each image plane may be set (e.g., set the DPIfor each image display plane/level), and the user may also set the coneangle and, in some cases, the mirror size. Step 730 may also includesetting the height of each image display level/plane (which also setsthe spacing between adjacent pairs of the planes/levels).

The method 700 continues at 740 with selecting or identifying a set ofmirrors in the array to use to display each of the pixels in the imageschosen in step 720 (with more detail provided for this process providedbelow). Step 740 may involve determining the number of mirrors thatshould be used for each pixel (typically a number between 1 and 40 ormore that is used throughout the design) based on a cone angle, mirrorsize, and the DPI of the image (or pixel pitch). In someimplementations, a program implementing the method 700 provides theaverage number of mirrors per pixel after step 730, and the user maydetermine it is useful to modify the design parameters (repeat step 730)to achieve a better result (e.g., some prototyping indicates that a“sweet spot” may exist around 25 mirrors per pixel with 10 being too fewin some cases and 40 being too many in others). Step 740 may alsoinvolve defining a cone with an apex coinciding at the pixel locationand with a cone angle set by the design parameters, and the cone base orarea on the mirror plane may be used to define which micro mirrors maybe chosen to display or “write” the particular pixel. The designparameters also define how many mirrors among the available ones in thiscircular or cone base area to use in the set of pixel-providing mirrors.A first mirror is chosen randomly (any useful random selection algorithmmay be used and it may have “memory” in that a next run may rememberwhich mirrors in the available set have already been chosen), and thenthis random process is repeated for the available mirrors until the setincludes the number of mirrors needed for a complete set based on thedesign parameters for this array of micro mirrors.

At step 750, the method 700 includes for a next one of the pixels in theimages, calculating angular orientation of all mirrors in the set ofmirrors chosen for displaying that pixel. At 760, it is determinedwhether there remain additional pixels in the images, and, if yes, themethod 700 proceeds with repeating steps 750 and 760 until all theangular orientations for the mirrors in the sets of pixel-providingmicro mirrors are determined. If no at step 760, the method 700continues at 770 with directing all mirrors not in one of these sets (orunused mirrors) so that they do not interfere with image display, e.g.,by assigning an angular orientation that is outside the viewing cone foreach of the pixels used to display the images on each of thelevels/planes.

At step 780, the method 700 is shown to include a decision step based onthe number and/or location of the unused mirrors. The method 700 (orcomputer program functioning to implement the method 700) may plot theposition of all the unused mirrors. If there are too many unused mirrors(e.g., above a predefined maximum unused mirror number) and/or theunused mirrors are too close to each other (e.g., not scattered over thecanvas or array of micro mirrors), the method 700 may return to step 730to change the design parameters and repeat the other steps of the method700 after step 730. The parameters that may be changed at 730 caninclude the cone angle (e.g., to have more surface from which to choosemirrors) and the height of the floating images (e.g., the closer theimages are floating to the mirror plane the more difficult it can be tofind useful mirrors so that higher or lower display/floating levels orplanes will decrease the number of unused mirrors). In some cases, theDPI can be changed from the original image and/or the image design mayneed to be changed to obtain a useful result with method 700.

If the number and/or location of the unused mirrors is determined to besatisfactory at 770, the method 700 then may end at 790. The design ofthe angular array may then be output for use in fabricating a securityelement with an array of micro mirrors individually oriented to provideone or more images (with a number of displayed pixels) on one or moreimage display planes/levels.

As discussed previously, an underlying idea of the security elements ofthe present description is to use ambient light and a planar surfacecontaining many small mirrors and to aim the ambient light reflected offthe mirrors toward a desired point in space above the planar surfacethat contains the mirrors. This is called the first layer image and isdefined by artwork that has light or dark pixels to be produced in alayer or level (or first image display plane). By carefully selectingthe mirrors within a circle defined by the intersection of the conedefined by an apex angle and a pixel from the first layer/level as theapex of the cone, the cone apex from various mirrors in the circularbase of the cone provides a point source of light floating above thelevel of the mirror plane at the location of a pixel, containing themirrors. A computer algorithm (as shown with the program 630 in FIG. 6)completes this process on a pixel-by-pixel basis. If the pixel in thefirst layer/level is a dark pixel (e.g., a pixel not associated with theimage or image component/portion from a base/start image chosen fordisplay in the first image display plane), no rays will be aimed towardit.

In addition, the program has the capability of using a second layer ofpixels that acts as a mask for the first layer of pixels so that variousportions of the pixel image at level one are “hidden” or visibledepending on the viewing angle. The algorithm that generates the firstlayer of floating pixels looks at the rays aimed to the pixel in thefirst layer and the continuation of the rays to the second layer. Theintersection location in the second layer is calculated and is searchedfor nearby dark pixels of the second layer/level (mask layer and/orsecond image display plane). If dark pixels are found in theintersection area on the second layer, the mirror that reflected thatray to the first layer is not used to aim the ray at that pixel to thefirst layer (e.g., this additional processing can be used to modify ororiginally select the mirrors to be used to display the pixel of thefirst image display plane).

Thus, there is a masking effect of the mask layer as is desired. To forma mask that appears to “float” over the pixels in the first layer (orfirst image display plane), some pixels of the first layer will havepartial cones of pixels depending on the mask geometry defined by thepixels on/off of the second layer and on the angle the pixels are viewed(as can be seen with reference to the diagram 400 of FIG. 4). As theviewer's eye is moved (or the mirror assembly tilted to the viewer),pixels of the first layer will change brightness and appear or disappearfrom view in a way that causes the mask to appear to move.

To insure uniform illumination across pixels, during the aiming processas described above, only one of the available mirrors is used in eachpixel's cone of acceptance by the design program, and the mirror isselected at random from the available mirrors in the cone of acceptance.After the direction cosines of the selected mirror are calculated, themirror is marked by the design program as “no longer available for useby any other pixel.” The design program moves on to the next pixel, andthe same sequence of events or design steps are repeated until all thepixels are used (or oriented for desired light reflection). At thatpoint in the design algorithm, the entire sequence of pixels is againused to pick up one of the available mirrors for each pixel. After anumber of cycles of the pixels, all the mirrors are used depending onthe image and mask patterns. If some mirrors cannot be used because ofthe geometry of the image layer and mask layer, they will be aimed outof the viewing zone.

The design program allows the user to choose the values of the spacingof image levels from the mirror plane, as well as pixel cone angles,mirror sizes and pixel pitches. These all can be optimized or selectedby the user to make (or try to make) the best image to present to theviewer. The inputs to the design program in some embodiments are pixelimage files for the first layer image and for the mask for the secondimage display plane or layer/level. However, there are also capabilitiesfor the program to make its own test input layers. The output of theprogram is a data file containing mirror locations and the coordinatesof the normal vector to each mirror in a format suitable to make themirrors or to form an array of micro mirrors on a supporting substrate(such as a piece of currency, a coin, a product label, a document, orthe like).

In some embodiments, the design program allows the user to see the inputfiles, ray traces to different levels (e.g., via operation of the raytracking module 635 shown in FIG. 6), and the expected image seen on theretina of a viewer. Tracings can be done using input cones of light onthe mirrors to see the affects ambient light distributions on theviewer's retina. As an example of the GUI 628 of FIG. 6 that can begenerated by the design program 639, FIG. 8 illustrates a micro mirrordesign GUI 800 that is displayed in one prototype of the design programcreated and used in prototyping by the inventors.

The main GUI or menu 800 shows an exemplary set of inputs (designparameters, for example) that can be chosen, input, or modified by theuser. These include pixel pitch, level/image display plane values, andcone angles for pixels, mirror size, and selection of test patterns. Theright side of the GUI/menu 800 shows some of the details or results ofthe calculations performed by the design algorithm based on the user'sinput or selected (or default) design parameters provided on the leftside. These include the number of mirrors that are dark (aimed away frompixels of images chosen for display on level or image display plane),numbers of mirrors used, algorithm used, and time required to calculatedirection cosines of mirrors.

The level height parameter can be used to define or set how far above orbelow the mirror plane, in microns, that the image designated willappear for a mirror array design. The level cone angle degree parametersets the angle at the floating pixel of the cone in which specificmirrors can be selected. A narrower angle means that there will be fewerpotential mirrors for each pixel, and the opposite for a larger angle.The level angle offset parameter defines or sets the angle of offsetthat you would like the image level to appear, in respect to the Z axis.The “Assign Image (1, 2) color (0, 1, 3, 4) to level #” input box allowsthe user to place the various image colors to the specified levels. The“Border Edge Width Add” input box allows the user to expand or shrinkthe canvas to allow for movement of the images.

As noted earlier, the design process begins with inputting or providingan image file for the design program to process to create or calculatethe design for the micro mirrors. One significant parameter in suchdesign calculations is the resolution (DPI), and, in some applications,it may be useful to input or use lower resolution files (or digitalimages). For instance, an image that is 100 DPI is equivalent to havinga pixel every 254 microns, and in the GUI 800 in FIG. 8 this is theinput shown under “image focal points×pitch=254” (and the same value forY pitch). Based on this resolution or how many pixels you need floatingto represent that specific image along with the mirror size (in theattached menu 800 this is 50 microns), the design program calculates“avg Num Mirrors available per pixel,” which in this example is25.7685291. In other words, a little over 25 mirrors that can be used torepresent one pixel from the original or base/starting image file.

FIGS. 9A-9C illustrate with graphs 910, 920, 930 images that can bedisplayed on various levels or image display planes by an array of micromirrors of the present description. Graph 910 of FIG. 9A shows a firstlayer image, with the light or on pixels providing an “X” pattern thatwould be displayed by a number of sets of pixel-providing mirrors to befloating in a first image display plane. In FIG. 9B, graph 920 shows asecond layer image, with the light or on pixels providing a rectangularbackground pattern or object that would be displayed by a number of setsof pixel-providing mirrors so as to be floating in a second imagedisplay plane. The graph 930 of FIG. 9C shows a partial “X” of light oron pixels displayed with micro mirrors of an array and shows the effectof a mask blocking part of the image.

FIG. 10 is a plot 1000 illustrating a ray tracing of light rays 1015 anddark rays 1017 near a first image display plane or first level/layer1020 for one modeled array of micro mirrors 1010. As can be seen, thearray of micro mirrors 1010 provides converging rays of reflectedambient light meeting or intersecting at a number of pixels 1022 at thefloating pixel level or image display plane 1020 (or a first level asdiscussed above). It can also be seen that dark rays 1017 are directedaway from the converging points/pixels 1022 and do not converge at thefirst level 1020.

One useful analysis tool of the design program and/or the ray tracingmodule is that a designer of an array of micro mirrors for a securityelement is able to evaluate the image as seen by a viewer. To this end,a ray tracing part of the design module (or a separate module as shownin FIG. 6) is used to view the image on a simulated retina. Thus, theeffectiveness of array design including a mask can be analyzed byputting the viewer's eye in various locations, which is equivalent totilting the mirror plane, and plotting the ray traced image on thesimulated retina. FIG. 11 illustrates a representative GUI or raytracing menu 1100 that allows a user to specify parameters to utilize inperforming the ray tracing. FIG. 12 illustrates a plot 1200 of arepresentative ray tracing showing the mirror plane 1210, tracedreflected rays/beams 1220, a face plane 1230, location of a viewer'seyeball at 1240, and a corresponding retina at 1245 upon which raysconverge indicating display of a set or number of pixels of a “written”or displayed image by the mirrors oriented in a desired manner at theplane 1210.

A number of manufacturing approaches may be used to fabricate an arrayof micro mirrors for attachment to or upon a surface of a substrate(such as currency, coins, product labels, and so on). In someembodiments, a photo resist process has been implemented by theinventors in creating security elements or devices as taught herein. Asdiscussed earlier, the design program or software generates an outputfile (as explained in more detail below). To form the micro mirrorsaccording to this output file, a laser system is used to expose thephoto resist material, usually on a quartz or lime glass master. Thephoto resist material is normally at least 25 microns thick. The laseror laser system may expose the material in steps such as in about 0.5μsteps. The exposure settings correspond to the amount of material thatwill be washed away and not hardened, and this exposure creates a “Z”axis or height of the feature. The resulting micro mirrors (which may beflat or may be concaved for better focus depending upon design) are madein the photo resist material. The photo resist is generally still lightsensitive and will “melt” in white light. In some cases, the photoresist is chrome plated in house before processing. The photo resist isthen placed in an electroforming tank. The resist is charged andattracts nickel (or other metallic) particles, and nickel is “grown” onthe photo resist as a nickel “shim.” This nickel shim can be “turned” asneeded from negative to positive and back again for tooling. The nickelshim is then used in the cast and cure process to form the array ofmicro mirrors oriented as indicated by the output file of the designprogram or software.

In other fabrication processes, a UV (ultraviolet light) or energy-curedpolymer is used, and the process includes metallizing the mirrors toform an array as taught herein. In other cases, the fabrication processinvolves stamping or forming the micro mirrors into surfaces such aschrome or aluminum containers.

In general, the inventors teach a method of fabricating a security orbranding element. The method includes providing a substrate and formingan array of micro mirrors on a surface of the substrate. The array ofmicro mirrors is configured for receiving ambient light and, inresponse, displaying an image in a plane spaced a distance apart fromthe surface of the substrate. The image comprises a plurality of pixels,and the array of micro mirrors includes for each of the pixels a set ofthe micro mirrors each having a reflective surface oriented to reflectthe ambient light toward a point on the plane corresponding to one ofthe pixels.

In some embodiments of the fabrication method, the forming the array ofmicro mirrors step includes casting the micro mirrors with a mirror toolin contact with the surface of the substrate. In these embodiments, thesubstrate may be a clear, energy-cured polymer, and the mirror tool canbe formed of nickel or a polymer.

In some cases, the step of forming the array of micro mirrors includesmetallization of surfaces of the micro mirrors. This may be performed soas to apply a thin layer of aluminum, gold, or silver to form reflectivesurfaces or form the mirror structures of the array. The metallizationmay be performed in a vacuum chamber using a deposition system or thelike. Further, the forming step may include, prior to the metallizationof the surfaces of the micro mirrors, embossing the surface of thesubstrate to form the surfaces of the micro mirrors. In this regard, itmay be useful for the surface of the substrate to include or be made upof an embossable coating or layer.

In performing the fabrication method, the substrate may be (or includeor be provided on) a coin, an automobile part, a computer part, abumper, or a container, and the displayed image provides branding orauthentication for the component that includes the array of micromirrors. In such cases, the array forming step may include stamping themicro mirrors into the surface of the substrate.

In the same or other embodiments, the step of forming the array of micromirrors may involve filling in recessed surfaces associated with themicro mirrors with a filler so as to make duplication (e.g., by molding)more difficult if not impossible. The filler may take the form of anultraviolet (UV) varnish, an e-beam solvent, a water-based varnish, orthe like. In some cases, it may be desirable for the filler to have ahigher refractive index such as an index of at least 1.55, such that atleast a portion of the received ambient light at extreme angles isreflected to sharpen the displayed image for a viewer.

From the description and figures, it can be seen that there are numerousadvantages and unique features of security elements/devices that includeor are formed of arrays of micro mirrors. The individual mirrors can beprogrammed or oriented in two axes to focus to a specific pixel in anyvisual plane (e.g., in a first image display plane, in a second imagedisplay plane, and so on). In this way, the micro mirrors are used toimage pixels forming drawings or text that appear to float relative tothe planar surface containing the array of micro mirrors. The micromirrors can be configured or designed to focus above or below the visualplane forming pixels that in combination display images with depth(multi-layered or multi-depth imagery). The program performs a uniquedesign method providing an output file that can be used in fabricatingor generating the micro mirrors.

In practice, the shape of the micro mirrors can be round, square, andrectangular with the reflective surface being flat, concave, or convexto provide desired focusing upon a pixel (or location on one of theimage display planes). The size of the mirrors may vary to practice thearrays of micro mirrors such as from about 1000 microns down to onemicron with mirrors in the 35 to 70 micron range likely being desirable(with 50 micron square mirrors being used in a prototype/model).

An array of micro mirrors can be designed to provide a variety of visualeffects such as showing images above or below the visual planes and infirst, second, third, or more image display planes relative to themirror-containing planar surface. In other cases, the mirrors are usedto provide an effect of light images with dark backgrounds animating tolight backgrounds and dark images with a change of perspective. In thesame or other cases, an array of micro mirrors can be configured withselective orienting of mirror reflective surfaces to provide a maskingeffect showing one image receding as it goes across another image. Inmany cases, the micro mirrors generate more than one level of imagery tothe viewer (two or more). Particularly, the micro mirrors can generateone image made up of a set of pixels at one level above the focal planewhile also (or separately) generating an image below the focal plane. Inthe same or other cases, the micro mirrors may be configured to generatean image at the focal plane. In these embodiments, the images aredisplayed/written either with bright pixels (light) or dark pixels (theabsence of light or reflected light from the viewer). Images created bythe micro mirrors can provide an animation effect, and, in the same orother embodiments, the images created by the micro mirrors may provide a3D effect.

The array of micro mirrors can be used in (or provided as part of) acurrency thread, which may be about 10 to 50 microns thick. The array ofmicro mirrors or security element can be used as a foil stamp that maybe about 10 to 100 microns thick. The array may be formed by stampingthe micro mirrors into any metallic surface, such as a surface of acoin, or by placing the micro mirrors on glass, ceramic, or plasticsubstrates, which may be clear so as to create a unique visual displayor imaging effect that allows a viewer to see images in display planeson two sides of the substrate supporting the array of micro mirrors (ortransparent film including such mirrors). In these and other ways, anarray of micro mirrors may be successfully used in any high securityapplication including, but not limited to, passports and other highsecurity documents including currency.

In some embodiments, the displayed or written image is colored (e.g., isnot simply black and white). In one embodiment, a color display iscreated by forming the mirrors of the array with plasmonic resonance forcolor while other fabrication processes use tinting of the reflectivemirrors with ink. In other embodiments, diffractive material is added tothe reflective surface of the mirrors or diffraction grating may be usedto create color with the micro mirrors. In some embodiments, dielectricsare used to provide color with the array of micro mirrors. In stillother colored display embodiments, a protective cover layer may beapplied to the mirrors that is transparent (to-translucent), and thencoloring may be provided by printing on this cover layer withtranslucent color squares (or other mirror shape-matching coloringfilters) aligned over the proper micro mirrors to achieve a desiredcolored image in one or more of the image display planes orlevels/layers.

FIGS. 13A and 13B illustrate plots 1310 and 1320 provided by the designprogram of images chosen for display on first and second image displayplanes or levels, respectively, and these are the two images that wouldbe written or displayed by micro mirrors of an array. In FIG. 13A, auser has input an image with a colored or plain background with acircular boarder enclosing a leaf, and the circular boarder and theoutline of the leaf have been chosen for display or writing on a firstlevel or first image display plane (at a first height such as 10000microns away from the planar surface containing the mirrors). The offsetangle may be set at 0 degrees (or some other value), and FIG. 13Arepresents an approximation of what a viewer would see when viewing thesecurity element with this design of an array of micro mirrors.Particularly, a plurality of bright or “on” pixels showing the circularboundary and the outer edges/boundary of the leaf.

FIG. 13B shows the first layer imagery 1310, but it also shows with plot1320 that as the viewer rotates the mirror plane or changes theirperspective (e.g., from a 0 degree viewing angle to the offset anglethat may be 20 degrees or the like) the original images 1315 arereplaced with the new images 1325 at the second level or second imagedisplay plane (which may be at 20000 microns or some other height suchthat the two levels/image display planes are spaced apart some desireddistance). As shown, the designer/program user has indicated that thebackground of the input image, the inner portion of the circle, and theinner portion of the leaf should be written or have their associatedpixels “on” in the second layer while the portions chosen for image 1315of the first layer are “off” or dark. In this manner, the image sees atransition between displaying imagery with light and then with darkpixels as their perspective or viewing angel changes to view the imagesin the two spaced apart levels/layers or image display planes.

FIGS. 14A and 14B illustrate plots 1410 and 1420 that show the resultsof programming or orienting an array of micro mirrors to display anobject or image 1415 (here an eagle or hawk). The plot 1410 of FIG. 14Amay be considered a top view as the intersections of normal vectors fromthe micro mirrors are shown relative to X and Y axes while the plot 1420of FIG. 14B may be considered a side view as the same intersections areshown relative to the X and Z axes. FIG. 14A is useful for showing arepresentation of what a viewer would perceive when looking in anorthogonal direction to the plane containing the mirrors, e.g., theviewer perceives the outline of an eagle (which may be displayed orwritten with bright or dark pixels). The intersections act to display“pixels” that, as can be seen at 1415, work in combination to display anobject/subimage (as may be chosen by a user of the design program froman input image file for display in a particular level or image displayplane). FIG. 14B shows that the pixels (or normal vector intersections)are generally planar or provided in a plane coinciding with apreset/defined level or image display plane relative to the planarsurface containing the micro mirrors (e.g., a plane spaced apart apredefine distance from the array of micro mirrors), and this acts toprovide a floating image 1415 or an image with depth or 3D effects.

As discussed above, the design program or algorithm functions to createan output file that may be used in manufacturing an array of micromirrors adapted to display one or more floating images above (or below)the planar surface containing the array. Table 1 below providesexemplary data that may be provided in such an output file (with only asmall number of mirrors being shown for ease of explanation but with itunderstood that similar data would be provided for each mirror in thearray). The X and Y columns of Table 1 show mirror positions (inmicrons), e.g., in the second row a mirror is located in the array at 35microns on the X axis and at 0 microns on the Y axis. In the table, nextto each mirror location in the array, the DX, DY, and DZ columns providethe coordinates of the normal vectors for each of the mirrors. In thisway, each mirror has a defined position in the array and a precisedirection its reflective surface is pointing in space.

In creating the exemplary data in Table 1, the following assumptionswere made for the design of the array of micro mirrors: (1) units aremicrons; (2) the array is configured to have flat mirrors with tiltedreflective surfaces; (3) the mirrors were square in shape with 35 micronsides; (4) the array was also assumed to be square in shape with 27,930micron sides; (5) the number of mirrors was calculated to be 798 alongthe X and Y axes such that the total number of mirrors was 636,804; and(6) the maximum mirror tilt angle was requested to be 30 degrees (e.g.,due to vendor/manufacturer limitations so may be set at 20 degrees).

TABLE 1 X Y DX DY DZ 0.00 0.00 −0.061672 0.021122 0.997873 35.00 0.00−0.020315 0.050724 0.998506 70.00 0.00 −0.063424 0.008449 0.997951105.00 0.00 −0.064293 0.008449 0.997895 140.00 0.00 −0.056737 0.0169040.998246 175.00 0.00 −0.053402 0.000000 0.998573 210.00 0.00 −0.0584820.012677 0.998208 245.00 0.00 −0.025586 0.008464 0.999637 280.00 0.00−0.051801 0.000000 0.998657 315.00 0.00 −0.061093 0.012675 0.998052350.00 0.00 −0.061967 0.004225 0.998069 385.00 0.00 −0.058619 0.0169020.998137 420.00 0.00 −0.046852 0.000000 0.998902 455.00 0.00 −0.0181420.004233 0.999826 490.00 0.00 −0.061225 0.021122 0.997900 525.00 0.00−0.062100 0.016898 0.997927 560.00 0.00 −0.062979 0.000000 0.998015595.00 0.00 −0.063848 0.004225 0.997951

FIGS. 15A and 15B illustrate plots generated and displayed by a previewprogram (which may be a subroutine of the design program describedherein) for previewing likely or predicted results of a design of anarray of micro mirrors. Specifically, FIG. 15A illustrates a plot 1510of a 3D image that may be displayed with a selected image and aparticular design of an array of micro mirrors. The plot 1510illustrates a foreground or first layer image 1514 (e.g., a bird such asa flying eagle) relative to a background or second layer image 1518(e.g., a colored frame with stars) relative to each other and X and Ycoordinates. The plot 1510 previews what a viewer looking directly at ordownward at the security device may see via the array of micro mirrors.FIG. 15B illustrates a plot 1520 illustrating the foreground image 1514and background image 1518 not only relative to the X and Y axes but alsorelative to the Z axis (e.g., the depth that would be provided by thearray of micro mirror design).

The preview program providing the plots 1510 and 1520 takes as input theoutput file of the design program, with all the mirror positions andnormal vector coordinates. The preview program calculates theintersection of the reflected rays (e.g., rays coming straight down andbouncing out of the mirrors to the viewer) with the plane where theimage is supposed to (or is designed to) float. With the plots 1510 and1520 provided by the preview program, the operator or designer canverify the combination of foreground and background images 1514, 1518provides a desired 3D image or representation as shown in FIGS. 15A and15B. In this example, an eagle 1514 is floating in a first image planeat +30,000 microns above the mirror plane while the frame 1518 (withstars) is floating in a pushed back second image plane at −30,000microns (or the two image planes are spaced apart 60,000 microns for theviewer providing a desirable 3D effect). Stated differently, the previewprogram takes the normal vectors corresponding to the eagle's mirrorsand plots the intersection to the plane at 30,000 microns (and does asimilar processing for the frame/background image's mirrors and theplane at −30,000 microns).

Although the invention has been described and illustrated with a certaindegree of particularity, it is understood that the present disclosurehas been made only by way of example, and that numerous changes in thecombination and arrangement of parts can be resorted to by those skilledin the art without departing from the spirit and scope of the invention,as hereinafter claimed.

We claim:
 1. A method of fabricating a security element, comprising:assigning a first object in a starting digital image to a first imagedisplay plane and a second object in the starting digital image to asecond image display plane; with a processor of a computing device,executing code to provide an array design module that operates to selecta set of micro mirrors in an array of the micro mirrors to display eachof the pixels of the first object in the first image display plane andto display each of the pixels of the second object in the second imagedisplay plane; for each of the pixels, determining with the array designmodule an angular orientation of each of the micro mirrors in theselected sets of the micro mirrors; and generating a design output fileincluding the angular orientation and location coordinates in the arrayfor each of the micro mirrors in the selected sets of the micro mirrors.2. The method of claim 1, wherein the angular orientation is defined bycoordinates of a normal vector from a reflective surface of each of themicro mirrors directing light to one of the pixels.
 3. The method ofclaim 1 wherein each of the sets of micro mirrors are selected randomlyfrom a plurality of the micro mirrors located in a base of a cone on asurface containing the array of micro mirrors.
 4. The method of claim 3,wherein the cone has an apex coinciding with coordinates of one of thepixels on the first or second image display planes.
 5. The method ofclaim 1, wherein the angular orientations are calculated based onheights of the first and second image display.
 6. The method of claim 1,wherein the angular orientations are calculated to provide a predefinedangular offset of at least 10 degrees between the first and second imagedisplay planes.
 7. A method of fabricating a security element,comprising: with a processor of a computing device, executing code toprovide an array design module configured to select a set of micromirrors in an array of the micro mirrors to display pixels of a firstobject in a first image display plane and to display pixels of a secondobject in a second image display plane spaced apart from the first imagedisplay plane; for each of the pixels, determining, with the arraydesign module, an angular orientation of each of the micro mirrors inthe selected sets of the micro mirrors; and generating a design outputfile including the angular orientation and location coordinates in thearray for each of the micro mirrors in the selected sets of the micromirrors, wherein each of the sets of micro mirrors are selected randomlyfrom a plurality of the micro mirrors located in a base of a cone on asurface containing the array of micro mirrors.
 8. The method of claim 7,wherein the cone has an apex coinciding with coordinates of one of thepixels on the first or second image display planes.
 9. The method ofclaim 7, wherein the angular orientation is defined by coordinates of anormal vector from a reflective surface of each of the micro mirrorsdirecting light to one of the pixels.
 10. The method of claim 7, whereinthe angular orientations are calculated based on heights of the firstand second image display.
 11. The method of claim 7, wherein the angularorientations are calculated to provide a predefined angular offset of atleast 10 degrees between the first and second image display planes. 12.A method of fabricating a security element useful on paper and coincurrency and on product labels, comprising: with a processor of acomputing device, executing code to provide an array design moduleconfigured to define an array of micro mirrors to be formed on a surfaceof a substrate; and generating a design output file including an angularorientation and location coordinates in the array for each of the micromirrors, wherein the array of micro mirrors is configured, when formedon the surface of the substrate, for receiving ambient light and, inresponse, displaying an image in a plane spaced a distance apart fromthe surface of the substrate, wherein the image comprises a plurality ofpixels, and wherein the array of micro mirrors includes for each of thepixels a different set of the micro mirrors each having a reflectivesurface oriented, in a fixed manner with a body of each of the micromirrors rotated about at least one of first and second rotation axesextending through the body, to reflect the ambient light toward a pointon the plane corresponding to one of the pixels.
 13. The method of claim12, wherein a voxel is created at each of the point on the plane viaintersection of two or more beams of the reflected ambient light, andwherein each of the created voxels produces an effect of a point sourceof light floating above the surface of the substrate in the plane. 14.The method of claim 12, wherein each of the different sets concurrentlyreflect the ambient light to concurrently generate the plurality ofpixels.
 15. The method of claim 12, further comprising providing thesubstrate and forming the array of micro mirrors by casting the micromirrors with a mirror tool in contact with the surface of the substrate,16. The method of claim 15, wherein the substrate provided in theproviding step comprises a clear, energy-cured polymer.
 17. The methodof claim 12, further comprising providing the substrate and forming thearray of micro mirrors by metallization of surfaces of the micromirrors, wherein the metallization applies a layer of aluminum, gold, orsilver to form reflective surfaces.
 18. The method of claim 17, whereinthe forming the array of micro mirrors includes, prior to themetallization of the surfaces of the micro mirrors, embossing thesurface of the substrate to form the surfaces of the micro mirrors andwherein the surface of the substrate includes an embossable coating orlayer.
 19. The method of claim 12, further comprising providing thesubstrate and forming the array of micro mirrors by filling in recessedsurfaces associated with the micro mirrors with a filler comprising atleast one of an ultraviolet (UV) varnish, an e-beam solvent, and awater-based varnish.
 20. The method of claim 19, wherein the filler hasa refractive index of at least 1.55, whereby at least a portion of thereceived ambient light at extreme angles is reflected to sharpen thedisplayed image.